In assembling a mount that aligns optical elements along an axis, such as a lens mount, that includes a plurality of parts, the distance along the axis of the mount from, for example, a lens frame that holds a lens system to a flange or stopper portion of a separate holder may need to be set with high precision. For example, the distance may need to be precisely set in order to locate the image detecting surface of an image detecting element, such as a CCD (charge coupled device). However, that distance may vary from a design value because of the nature of the design and the tolerances in various dimensions of the frame and the holder. For this reason, adjustment of the distance is performed at various assembly steps of the mount, which may be a lens mount as described above.
In a conventional mount for optical elements, such as that disclosed in Japanese Laid-Open Patent Application 2000-184262, the distance to the flange or stopper portion is adjusted by screwing a back focus adjustment ring on a lens holder to which a lens is attached. Rotation of the focus adjusting ring moves an image detecting element along the optical axis of the lens relative to the lens and thus the distance to the flange or stopper that determines the distance to the image detecting surface is adjusted. A coil spring operates between the lens holder and the back focus adjustment ring to remove any backlash in the screw connection.
However, the use of a coil spring for removing backlash as disclosed in Japanese Laid-Open Patent Application 2000-184262, not only requires an added separate element (i.e. the coil spring) but is also disadvantageous in that the bias force exerted by the spring changes with the amount of adjustment. Additionally, in most cases, the back focus adjustment ring is anchored on the lens holder by adhesive, or similar connections, after adjustment. Therefore, further adjustment based on rotation of the back focus adjustment ring and use of the coil spring is impossible, which is also a shortcoming of this solution.
The present invention relates to a mount for optical elements, such as a lens mount, that uses a screw connection between a frame and a holder, such as a lens frame and a lens holder, that allows precision adjustment of the distance from the frame to a flange or stopper that determines the position of another optical element, such as an image detecting element, and that avoids problems of backlash in the screw connection in a simple manner.